The present invention relates to magnetic recording-reproduction devices, such as VCRs (video cassette recorders), wherein the tape speed and phase can be controlled for the reproduction of video signals by recording a control signal on the control track of the magnetic tape.
The so-called time lapse VCR is already known as a signal recording device for use as connected to a monitoring camera installed in a store or the like for security purposes. It is sometimes compulsory to set a specified preservation period for the magnetic tape having video signals recorded thereon by the time lapse VCR. Due to a careless error in the management of magnetic tapes, however, it is likely that video signals will be recorded anew on the magnetic tape of which the specified preservation period has not elapsed. Accordingly, a magnetic tape management method is known wherein tape management data such as the time and date of recording is recorded as superposed on the video signal during a vertical blanking period of the video signal and read from the tape when video signals are to be recorded.
However, this method requires an integrated circuit specifically for superposing the data on the recorded video signal and reading the data from the reproduced video signal, hence the problem of necessitating an increased circuit board area and an increase in the number of assembling steps.
Accordingly, an object of the present invention is to provide a magnetic recording-reproduction device which is adapted for the management of magnetic tapes without incorporating a specific integrated circuit conventionally needed.
The present invention provides a magnetic recording-reproduction device which comprises a CTL signal recording circuit 5 for recording a control signal on a magnetic tape, a CTL duty setting circuit 4 for setting a variable duty ratio for the control signal, a CTL signal reproduction circuit 6 for reproducing the control signal recorded on the magnetic tape, a CTL duty identification circuit 7 for identifying the duty ratio of the reproduced control signal, and a system control circuit 8 for controlling the operation of the device.
The system control circuit 8 comprises: first control means for decoding magnetic tape management information superposed on the control signal based on the result of identifying the duty ratio by the CTL duty identification circuit 7 when a command is given to record video signals and controlling validation/invalidation of the command according to the result of decoding, and second control means for commanding the CTL duty setting circuit 4 to vary the duty ratio to superpose magnetic tape management information on the control signal when video signals are to be recorded.
When a command is given to record video signals, playback of the control track is started at a specified location on the magnetic tape 1, and the CTL signal reproduction circuit 6 and the CTL duty identification circuit 7 operate to identify the duty ratio of the control signal reproduced from the control track. The magnetic tape management information superposed on the control signal is decoded based on the result of identifying the duty ratio, and the validation/invalidation of the command is controlled according to the result of decoding. Information as to the date when video signals were recorded on the magnetic tape can be included in the tape management information.
The first control means of the system control circuit 8 is accordingly capable of checking whether the decoded date indicates that a specified period has not elapsed, and invalidates the command for recording when the specified period has not elapsed. This obviates the likelihood that video signals will be recorded anew on the magnetic tape of which the specified preservation period has not elapsed.
Information as to the number of times video signals were recorded on the magnetic tape can be included in the magnetic tape management information. This enables the first control means of the system control circuit 8 to check whether the decoded number of times is in excess of a specified number of times. If the specified number of times has been exceeded, the second control means invalidates the command for recording. This eliminates the likelihood that video signals will be recorded anew on an old tape which is in excess of the specified number of times video signals were recorded.
According to a specific embodiment, the second control means of the system control circuit 8 issues a command to give an altered duty ratio to the control signal to be recorded in the vicinity of the starting point of the magnetic tape. If the tape is played back in the vicinity of the starting point in this case, the tape management information can be read from the tape at all time.
Further according to another specific embodiment, the second control means of the system control circuit 8 issues a command to give an altered duty ratio to the control signal to be recorded over the entire length of the control track of the magnetic tape, at a predetermined interval along the control track. The latest tape management information can then be read from a desired location on the magnetic tape even if it is an intermediate portion of the tape.
The CTL duty setting circuit 4, CTL signal recording circuit 5, CTL signal reproduction circuit 6 and CTL duty identification circuit 7 described are incorporated also in conventional VCRs, for example, for locating the start of a recorded sequence, so that the device of the invention can be provided merely by adding the functions (software) of the first control means and the second control means to the conventional system control circuit.
The magnetic recording-reproduction device of the present invention has a simple construction for effecting magnetic tape management without using a specific integrated circuit conventionally needed.